1. Field of the Invention
The present invention relates generally to production of compact discs (also known as "CDs"), and more particularly to a system and method for production of customized compact discs on demand.
2. Statement of the Prior Art
High fidelity was redefined for audiophiles as soon as they heard the pure digital sound of a compact disc (CD). The sonic range of plastic-coated CDs was so superior to the older "hi-fi" recordings that, by the 1990s, long-playing (LP) vinyl discs were becoming obsolete.
In the past, the production of a CD began with a high-quality sound recording on magnetic tape. Conversion of the constantly changing analog signal on such tapes into a digital signal made the CD markedly different from an LP, the factor that enhances audio reproduction. To digitize the signal, it was first converted into a series of electrical pulses.
Conventional digitization was done by electronic circuits that sample the analog signal about 40,000 times a second. These electronic circuits converted the strength of the signal at each of the samplings into a given number in the digital signal. A series of digital pulses was then fed to a "write" laser that illuminated portions of a photosensitive material applied to a master disc. Whenever there was a pulse in the signal, the laser burnt a small oval pit into the surface of the spinning disc. Eventually, an alternating pattern of such pits and "lands" (i.e., flat areas) remained on the master.
After the master disc had been so inscribed, the spiral series of pits and lands was then impressed on the molded plastic CD base. A layer of reflective aluminum was then applied to the label side and topped by a protective layer of plastic. The side opposite the label, as is typical, contained all the recorded information on the CD. The minuscule pits and the lands were arranged in a spiral line similar to the groove on a conventional phonograph record, but they were more closely spaced and capable of storing much more information. Unlike the grooves of an LP, however, the pit tracks on a CD originate near the center hole and spiral outward. A "read" laser was thereafter used to read the CD by starting on the inside and moving to the outside.
In the early 1980s the first CDs, which were nearly 5 inches (12.7 centimeters) in diameter, stored the same amount of sound on one side as a 12-inch (30.5-centimeter) LP reproduced on two sides. Such CDs could store and play back up to about 80 minutes of music. For shorter selections, there were also so-called "singles", that is, 3-inch (7.6-centimeter) discs comparable to 45-rpm records.
The CD advantage over LPs and audiocassettes went beyond accuracy of sound reproduction and longer playing time. Digital signals from an audio CD provide a greater dynamic range than analog signals from an LP or audiocassette (e.g., 90 decibels, compared to 70 decibels). Moreover, the groove-and-stylus mechanism of a conventional phonograph can damage recordings or alter their sound, and audiotapes often unravel. There is no physical wear and tear from the laser in a CD player, however, and dust and minor scratches cause almost no distortion. Accordingly, CDs have become almost universally popular.
Notwithstanding their popularity, one distinct problem which exists with currently available audio CDs is their limited selection. Buyers must go to the store or consult a catalog and purchase CDs having music in the order that is preselected by the production studio. There are no "one-offs". That is, there is a complete absence in the prior art of systems and methods for efficiently and cost-effectively producing custom CDs which are determined by the buyer's choice in music/artists.
The primary reason for such absence is that high-quality, digital audio data is very bulky. One minute of CD-audio data uses around 10 Megabytes of storage. Accordingly, a system storing 10,000 titles (or about 35,000 minutes of music), would need around 400 Gigabytes of storage space. While possible, using this amount of magnetic disc storage would be quite expensive when one takes into account the price of magnetic discs and the price of a computer big enough to manage those discs.
An alternative manufacturing approach to avoid this storage problem would be to store masters as removable media in jukeboxes. However, using removable media in automated libraries has the potential of introducing reliability and data availability problems. In order to manufacture at least one thousand custom discs per day with conventional CD recorders, for example, a CD production system would have to retrieve ten titles each minute. That is demanding, both in terms of library accesses and data transfer rate.
One solution to the aforementioned problems would be to compress the audio data to reduce the storage requirements. It has been found, furthermore, that the Motion Picture Experts Group (i.e., MPEG) audio compression standard is most effective when utilized in accordance with the present invention.